The present invention relates generally to medical devices and, more particularly, to a catheter having a soft tip and multiple lumens extending through the tip for passage of devices used, for example, to measure oxygen saturation of blood.
At present, catheters that have a soft tip designed to prevent puncture of a vessel wall are exclusively single lumen catheters. In these catheters, if multiple lumens are required they are limited to the catheter body and do not extend through the distal tip. Side ports proximal to the distal tip permit the fluid to be infused from the lumens. For example, central venous (CV) catheters have a soft, single lumen tip and are used primarily to gain access to the venous vasculature for fluid infusion, blood sampling and central venous pressure monitoring. CV catheters are inserted into the patient using the Seldinger technique. This involves identifying the target vein, puncturing the vein and inserting a guidewire. A vessel dilator is inserted over the guidewire and pushed through the vessel wall to create an opening for the CV catheter. The dilator is removed though the guidewire remains in place. The single lumen CV catheter is then threaded over the guidewire and pushed through the tissue and into the vessel. Importantly, the catheter is inserted without any stiffening members other than the guidewire. The tissue and vessel wall resist the catheter as it slides into the vessel. Therefore, to insure the catheter can easily slide into the body, the catheter body and catheter tip must be sufficiently rigid to slide over the guidewire into the blood vessel without buckling or otherwise collapsing. Once a CV catheter is placed into the blood vessel, then the stiffness that was desirable during insertion through the vessel wall becomes a disadvantage. Vessel perforation is always a concern in the design of these catheters. Another concern is that the catheter tip migrates from the central vena cava to the right atrium. The right atrium contains regions of thick and thin walls. During routine monitoring, if catheter has migrated into the right atrium, through the action of normal heart beats, and lodges into the heart wall in one of the thin walls sections, the catheter tip can punch through the atrial wall and create cardiac tamponade. If the superior vena cava above the pericardial sac is perforated, a pleural infusion is created, leaking fluid into the pleural or lung cavity. During use, a stiff catheter and tip increases the possibility of endothelial abrasion and vessel wall or right atrium wall perforation. Such perforation generally requires surgical intervention to resolve.
Because of these dangers, CV catheters typically include a soft distal tip that yields when it contacts a vessel wall, and a radiopaque marker is incorporated into the tip to monitor its location within the body. This reduces, but does not eliminate, the possibility of the catheter perforating the vessel wall during repeated contact during use. Therefore, CV catheters tips have been made with softer materials to yield more easily when contacting a vessel wall. Such tips are made of materials such as low durometer urethanes, for example Tecoflex and Pellethane, due to their high durability and ease of manufacturing.
Importantly, however, all commercially available CV catheters with soft distal tips have one common feature—their distal tip has only a single lumen which is used for passing a guidewire during insertion and later during the use of the catheter may serve for fluid infusion. Such a lumen extending through the distal tip does not have any medical implement, for example, a sensor or a probe, located within because it would compromise the flexibility of the soft tip and would also interfere with the passing of the guidewire during insertion. More than one lumen in the distal tip creates an asymmetry in the transverse cross-section and increases the chances of buckling. Therefore, CV catheters are uniformly constructed with a single lumen at the distal tip. Of course, any other type of catheters that requires such a soft tip are at present single lumen, not just CV catheters.
Typical pulmonary artery (PA) catheters, on the other hand, have blunt rigid tips because they are usually inserted through a vascular access introducer. Such an introducer has already been positioned within the target vessel, and includes a large bore port through which the PA catheter can be passed, and a hemostasis valve on its proximal end to prevent blood leakage around the catheter. Such stiff, flat tips are relatively easy to manufacture and facilitate polishing of the distal end of the optical fibers. Therefore, the above described PA catheters are known to include either single or multiple lumen rigid distal tip.
As a result, at present the only catheter tips available are either single lumen soft tip or single/multiple lumen rigid tip. Accordingly, there is a need for an improved catheter having a soft tip and multiple lumens extending through the soft tip.